FIG. 1 is a schematic side elevation showing a conventional general container crane in which reference numeral 1 denotes a container ship moored at a quay 2 to and from which a container 4 is loaded and unloaded by the container crane 3.
The container crane 3 comprises legs 6 on rails 5 for running along the quay 2, girders 7 atop of the legs 6 and extending substantially horizontally to protrude toward the sea, traverse rails 8 extending along the girders 7 and a trolley 9 for movement in traverse direction.
The trolley 9 comprises, as shown in FIGS. 2 and 3, a trolley body 11 with traverse wheels 12 for rolling on the traverse rails 8. Tied to the trolley body 11 are opposite ends of a traverse rope 13 which is wound around a traverse drum (not shown) in a machine room 10 (see FIG. 1) and which extends under tension longitudinally of the girders 7. Rotation of the traverse drum in normal or reverse direction causes the trolley 9 to be moved in traverse direction.
The trolley 9 has a head block 15 suspended from the trolley 9 through hoisting ropes 14 which in turn are wound around a hoist drum (not shown) in the machine room 10 and which extend under tension longitudinally of the girder 7. Rotation of the hoist drum in normal or reverse direction causes the head block 15 to be hoisted up or down.
Detachably interlocked with the head block 15 through twist locks 17 is a spreader 16 which grips the container 4.
The twist lock 17 comprises a lock pin 19 adapted to be inserted into a slot on an upper surface of the suspender 18 of the spreader 16 and adapted to be twisted for example by a hydraulic cylinder for interlock of the head block 15 with the spreader 16.
The conventional spreader 16 comprises, as shown in FIGS. 1, 3 and 4, extension frames 21 and 22 which are respectively fixed by retainers 21xe2x80x2 and 22xe2x80x2 to respective parallel portions of an endless chain 26 which in turn extends under tension longitudinally of the stationary frame 20. The chain 26 is driven by a drive 27 to extend or contract the lateral extension frames 21 and 22 in unison laterally or perpendicularly of the traverse direction of the trolley 9. Such extension or contraction of the extension frames 21 and 22 allow a variety of containers 4 with different lengths to be suspended.
Each of the extension frames 21 and 22 has, at its tip, twist locks 23 constructed similarly of the twist locks 17 of the head block 15 to grip the container 4 as well as guide arms 24 for positioning the twist locks 23 for engagement with the container 4. The guide arm 24 can be swung from an upper, turned-over open position into a position for engagement with a corner of the container 4 by actuation of a hydraulic motor 25. This will ensure that the spreader 16 can be correctly positioned to the container 4 and that the twist locks 23 can be positively engaged with the container 4 even if there may be some deviation in lowering the spreader 16 interlocked with the head block 15 onto the container 4 for hoisting of the container 4.
Each of the extension frames 21 and 22 of the conventional spreader 16 comprises, as shown in FIGS. 4 and 5, two frames each with a vertically elongated rectangular section, the two frames being spaced apart from and connected with each other widthwise of the stationary frame 20. The extension frames 21 and 22 are supported by sliders 21a, 21b, 22a and 22b (FIG. 5) such that they may brush past with each other with respect to the stationary frame 20. The extension frames 21 and 22 may be I-shaped frames other than the vertically elongated rectangular frames as shown in FIG. 5.
Generally, the container 4 is loaded onto the container ship 1, using the container crane 3, by the following sequence of operations. Firstly, the spreader 16 interlocked with the head block 15 from the trolley 9 is hoisted down onto the container 4. The rock pins 19 of the twist locks 23 are then inserted into slots on an upper surface of the container 4 and are twisted for example by a hydraulic cylinder to interlock the spreader 16 with the container 4. In this state, the head block 15 and spreader 16 are hoisted up and the trolley 9 is moved in traverse direction to a target position above the container ship 1. Then, the head block 15 and spreader 16 are hoisted down to place the container 4 onto the container ship 1.
In such container crane 3, the container 4 often has a predetermined destination. In such a case, with the destination of the container 4 being set, the trolley 9 may be automatically moved in traverse direction; and only hoisting-up and -down of the spreader 16 interlocked with the head block 15 may be manually carried out by an operator in an operation room 36.
However, the above-mentioned conventional spreader for the container crane has following various problems.
The spreader 16 tends to be damaged since generally the spreader 16 is collided with and placed onto the container 4 when the spreader 16 interlocked with the head block 15 is to be hoisted down onto the container 4 for connection of the spreader 16 with the container 4. More specifically, when the spreader 16 is hoisted down, only tip ends of the extension frames 21 and 22 contact the upper surface of the container 4, resulting in cantilever relationship of the extension frames 21 and 22 to the stationary frame 20. This means that when heavy weight (for example over 10 tons) of the head block 15 and spreader 16 acts on the extension frames 21 and 22 upon the collision, the extension frames 21 and 22 will receive extreme bending load which is, for example, 3 or 4 times as large as that received upon hoisting of the container 4. The conventional spreader 16, thus, tends to have damages such as bending of the extension frames 21 and 22. Bending of the extension frames 21 and 22 requires repairing since it disables the extension frames 21 and 22 from being slidingly extended or contracted and shortens the service life of the spreader 16.
In the conventional spreader 16, the lateral extension frames 21 and 22 are unaligned or out of alignment in their lateral axes as shown in FIGS. 4 and 5 so that the extension frames 21 and 22 may be twisted due to any eccentric or torsion load applied when the container 4 is hoisted by the spreader 16.
In order to prevent such bent and/or twist of the extension frames 21 and 22, the spreader 16 must be large in size and/or the stationary and extension frames 20, 21 and 22 must have increased thickness. However, these will inevitably cause increase in weight of the spreader 16, resulting in increase of electric power required for hoisting of the container crane as well as increase of operation cost.
It has been also conventionally envisaged that the stationary and extension frames 20, 21 and 22 have box-shaped sections for enhancement of their sectional strength. However, such box-shaped sections will not allow the extension frames 21 and 22 to be brushed against with each other as shown in FIGS. 4 and 5; and the extension frames can be hardly extended or contracted with greater stroke depending upon variation in length of the containers. Devised out to overcome this problem were lateral extension frames in the form of two-step extendable (telescopic) structure.
However, such lateral extension frames in the form of two-step extendable structure have been proved to be impracticable since the extension frames may be greatly bent and/or bowed and fail to retain their sufficient strength when the container is hoisted.
Furthermore, in the conventional spreaders 16, the extension frames 21 and 22 are slidably supported on the stationary frame 20 so as to be extended or contracted depending upon size of the container 4. More specifically, the stationary frame 20 supports the extension frames 21 and 22 via slide bearings (flat metal bushes).
As a result, friction coefficient between the stationary frame 20 and extension frames 21 and 22 is so large that greater friction force will be generated upon relative slide movement between them, which will necessitate increase in driving force of the drive 27, resulting in necessity of providing the drive 27 with greater rating. Thus, cost increase will be caused from aspects of both product price and electric power consumed. Contact surfaces between the stationary frame 20 and extension frames 21 and 22 must be machined with higher plane accuracy, resulting in increase in machining cost.
The present invention was made in view of the above and has its object to provide a spreader for a container crane which is light in weight, is free from bent and twist of extension frames, can reduce drive force required for extension or contraction of the extension frames and can relieve impact load applied to the extension frames of the spreader when the spreader is hoisted down onto a container.
A box body with a box-shaped section is provided with laterally extendable telescopic inner and outer box frames. This will drastically enhance bending rigidity of the inner and outer box frames in comparison with conventional spreaders. Moreover, because of telescopic type, the inner and outer box frames are aligned in their lateral axes to prevent twisting load from being applied on the inner and outer box frames, thereby enhancing the strength of the spreader to relieve any possible damages and to prolong the service life of the spreader.
The inner box frame is slidably supported in an end of the box body by inner supports arranged above and below of lateral axis of the inner box frame; and the outer box frame is supported in the other end of the box body by side supports arranged above and below and symmetrically of lateral axis of the outer box frame. The inner and outer box frames can be extended or contracted with greater stroke and with no mutual interference since notches are respectively formed on a top and a bottom of the outer box frame at its base end supported by the box body.
A stationary frame has lateral open ends each of which has at its lower portion support rollers each of which in turn accommodates a bearing and serves for receiving load of the corresponding lateral extension frame. This allows the support rollers to be in rolling contact with the extension frames upon extension or contraction of the extension frames so that only rolling friction is produced between them, resulting in drastic reduction of the drive force for extension or contraction of the extension frames.
The support roller is rotatably supported by arms each of which has one end pivotally supported by the stationary frame and the other open end rotatably supporting the support roller. The arm is kept urged upwardly by urge means such as a helical spring, a torsion bar or a blade spring. The urging force is set to an extent such that the support roller may push up the extension frame to receive the load of the extension frame and that the support roller may escape downwardly when the load of the container is applied. Thus, the support roller will have no greater load applied upon suspension of the container, preventing the support roller from being damaged.
The stationary frame has, at its surface facing to a surface of the extension frames, a rail which extends in the direction of extension and contraction of the extension frames. The extension frame has a rubber or other cushioning member and a slide fitting which rests on the cushioning member and is engaged with the extension frame so as to be fitted over the rail and relatively displaced thereto. Thus, the slide fitting is relatively displaced in guidance of the rail upon extension or contraction of the extension frames, and greater collision force received by the extension frames upon collision of the spreader with the container is absorbed by the cushioning members.